Solenoid valves of the type mentioned in the introduction are known from the prior art. The armature of a solenoid valve of this type can be influenced by a magnetic force, for example, by means of at least one coil in such a manner that the said armature is axially displaced and in so doing the valve element is arranged to open up or close off the valve seat. The armature and/or the valve element can in addition be operatively connected to a resilient element, which produces a resilient force that urges the armature and/or the valve element in the direction of the respective idle position and/or its starting position. The idle position can be an open position in which the valve element at least partially opens up the valve seat, or a closed position in which the valve element closes off the valve seat. A de-energized open solenoid valve is provided in the first case and in the latter case a de-energized closed solenoid valve is provided. The solenoid valve can be embodied, for example, as a high pressure switchover valve. Preferably it is used in a driver-assisting device, which is, for example, an ESP, ASR or an ABS system.
The solenoid valve comprises a first fluid connection and a second fluid connection for a fluid. If the solenoid valve is open, i.e. the armature is arranged to open up the valve seat, then the fluid can flow through the solenoid valve from the first fluid connection as far as the second fluid connection. If, on the other hand, the solenoid valve is closed, then the valve element is arranged to close off the valve seat, consequently closing the flow connection between the first fluid connection and the second fluid connection inside the solenoid valve. The first fluid connection of the solenoid valve is allocated, for example, to a wheel brake cylinder and the second fluid connection is allocated to a master brake cylinder of a braking system. As the brakes are applied, pressure builds up in the master brake cylinder and consequently also in the wheel brake cylinder. When the solenoid valve is open, fluid can flow out of the master brake cylinder in the direction of the wheel brake cylinder, on the other hand, when the solenoid valve is closed, the flow connection is closed.
In addition, the non-return valve is arranged so as to influence the flow between the first fluid connection and the second fluid connection of the solenoid valve. The non-return valve is provided for the purpose of allowing a through-flow between the first and the second fluid connection only in one direction, namely only from the second fluid connection to the first fluid connection. When the solenoid valve is open, the non-return valve is substantially non-functional. If, on the other hand, the solenoid valve is closed, then by virtue of the valve seat no fluid can flow between the first and the second fluid connection, however, by means of the non-return valve a flow connection is opened between the first and the second fluid connection. If, when the solenoid valve is closed, the pressure of the fluid that prevails at the second fluid connection exceeds the pressure that prevails at the first fluid connection, then the non-return valve opens so that the fluid can flow through the solenoid valve from the second fluid connection to the first fluid connection. If, on the other hand, the pressure on the side of the first fluid connection is greater or equal to the pressure on the side of the second fluid connection, then the non-return valve is closed.
Thus, the non-return valve generally only opens if both the solenoid valve is closed (because only in this case is there a difference between the pressure at the first fluid connection and the pressure at the second fluid connection) and the pressure at the second fluid connection is higher than the pressure at the first fluid connection. In this manner, it is possible for the prevailing pressure in the wheel brake cylinder to reduce when the solenoid valve is closed if the pressure prevailing in the master brake cylinder is lower than the pressure in the wheel brake cylinder. The solenoid valve is preferably a de-energized open solenoid valve that is used as an inlet valve of the driver-assisting device. The non-return valve is generally arranged in a separate component of the solenoid valve, which increases the overall size of the solenoid valve.